Dialog systems are being developed for open-domain chatting without a specified task. In comparison to a conversation system oriented toward a specified task, the content of the utterances of the user vary quite broadly for the open-domain dialog system, and thus the task of creating beforehand a knowledge source required for generating a suitable reply sentence is quite difficult.
In order to handle this problem, technology is disclosed for generating an utterance sentence by use of microblogs such as Twitter (registered trademark) for which there exist a large number of sentences (Michimasa Inaba, Sayaka Kamizono, and Kenichi Takahashi, “Candidate Utterance Acquisition Method for Non-task-oriented Dialogue Systems from Twitter”, Journal of Japanese Society for Artificial Intelligence, Vol. 29, No. 1, SP1-C, 2014). Further, Unexamined Japanese Patent Application Kokai Publication No. 2015-45833 discloses technology for generating an utterance sentence by extracting a term meaning a subject of utterance content from utterance content of a user and substituting the term into a template. Unexamined Japanese Patent Application Kokai Publication No. 2014-164582 discloses, in a system for dialog with a user by use of natural language, an utterance candidate generating device of a dialog system for generating an utterance candidate using a microblog.
Additionally, robots termed “personal assistants” or “dialog agents” are being developed that receive an utterance from a user and return a response to the user. A dialog agent is a robot that serves as a partner, located in the vicinity of the user, in a casual chat (for example, see Unexamined Japanese Patent Application Kokai Publication No. 2017-123187). Dialog agents also include applications fictitiously operating in the computer.